In a radio communications system, such as a Long Term Evolution (LTE) system or a Long Term Evolution Advanced (LTE-A) system, an orthogonal frequency division multiple access (OFDMA) manner is generally used as a downlink multiple access manner. Downlink resources of the system are divided into orthogonal frequency division multiplexing (OFDM) symbols from a perspective of time, and are divided into subcarriers from a perspective of frequency.
In a communications system, a normal downlink subframe includes two slots, and each slot has 7 or 6 OFDM symbols. A normal downlink subframe includes 14 OFDM symbols or 12 OFDM symbols in total. The LTE Release 8/9/10 standard also defines a size of a resource block (RB). A resource block includes 12 subcarriers on a frequency domain, and is half a subframe duration (that is, one slot) on a time domain, that is, includes 7 or 6 OFDM symbols. In one subframe, a pair of resource blocks of two slots is called a resource block pair (RB pair). In actual sending, a resource block pair used on a physical resource is called a physical resource block pair (PRB pair). To facilitate calculation of the size of resources included in each elementary resource block pair, a resource element (RE) is defined. A subcarrier on an OFDM symbol is called an RE, and an elementary resource block pair includes multiple RE groups: REG (Resource Element Group).
The mapping of all types of data borne in the subframe is organized by dividing physical time-frequency resources of the subframe into various physical channels. On the whole, various physical channels may be classified into two types: control channels and traffic channels. Correspondingly, data borne on a control channel may be called control data (which can be generally called control information), and data borne on a traffic channel may be called traffic data (which can be generally called data). An essential objective of sending a subframe is to transmit service data, and the control channel serves the purpose of assisting in transmission of the service data.
In an LTE system, when control channel transmission is performed, a complete physical downlink control channel (PDCCH) may be formed by aggregating one or more control channel elements (CCE). The CCE is formed by multiple REGs.
Due to introductions of technologies such as multi-user multi-input multi-output (MIMO) and coordinated multiple points (CoMP), a PDCCH transmitted based on a precoding manner is introduced, that is, an enhanced physical downlink control channel (ePDCCH). The ePDCCH may be demodulated based on a UE-specific reference signal, that is, a demodulation reference signal (DMRS). Each ePDCCH may be formed by aggregating up to L logical elements similar to the CCE, that is, enhanced control channel elements (eCCE). One eCCE is mapped onto M enhanced resource element groups (eREG) similar to the REGs.
It is assumed that an elementary resource block pair includes N eREGs, L eCCEs are mapped onto the N eREGs, and each eCCE is mapped onto M eREGs. Therefore, the method for mapping the L eCCEs onto the N eREGs in the prior art is: Fixedly, the first M eREGs of the N numbered eREGs correspond to an eCCE, and similarly, the next M continuous eREGs correspond to another eCCE, and finally L eCCEs are formed.
In fact, when the ePDCCH is mapped onto the eREG corresponding to each eCCE, because the number of valid resource elements varies between the eREGs after deduction of overhead such as a CRS (common reference signal), a PDCCH (physical downlink control channel), a PRS (positioning reference signal), a PBCH (physical broadcast channel), and a PSS (primary synchronization signal) or an SSS (secondary synchronization signal), the actual size of the M eREGs corresponding to one eCCE is imbalanced, which leads to imbalanced performance of demodulating each eCCE, and increases implementation complexity of a scheduler.